1. Field of the Invention
The invention relates generally to orthopedic surgical guides and jigs. More particularly, the invention relates to a slotted patella resection guide and stylus that may be used in the preparation of the human patella to accept a patella prosthesis in total knee arthroplasty. The slotted patella resection guide and stylus contemplated by the invention, when used in combination, enables the guide to be accurately placed at a level which assures a precise resection of a predetermined amount of bone.
According to a preferred embodiment of the invention, the resection guide has a plurality of calibrated and marked steps (slots), each located at a different fixed predetermined height above the desired resection level. Each slot is designed to accept the stylus which may be at least temporarily secured therein.
A surgeon, for example, once having determined the amount of bone to be resected, simply places and temporarily secures the stylus in the appropriate slot (the slot marked as being calibrated to yield the amount of resection desired); and then uses the resection guide contemplated herein, in a manner to be explained in detail hereinafter, to clamp onto the patella and guide a sagittal saw used to actually perform the resection.
Further aspects of the guide and stylus combination contemplated by the invention are (1) the quick attachment/release nature of the stylus itself, i.e, the stylus is easily attached to the calibrated and marked steps on the resection guide, and easily removable therefrom to enhance the surgeons visibility while performing the resection; (2) the jaws of the contemplated resection guide include a saw capture slot which defines the plane of resection and accepts the saw blade used to perform the resection, thereby providing greater control of the cut during the operation; and (3) a saw blade insertion guide mechanism is integrated into the patella resection guide. For example, the guide mechanism can take the form of a "ledge" where the saw blade enters the saw blade capture slot to ease the process of inserting the saw blade into the slot, provide support for the saw blade itself and enhance the safety characteristics of the instrument.
2. Description of the Related Art
The two largest and longest bones of the human body, the femur and tibia, meet at a person's knee. The tibia is situated at the front and inner side of the lower leg. It is prismoid in form, and expanded above where it enters into the knee joint. The head of the tibia is large and expanded on each side into two eminences, the condyles. These eminences form two smooth concave compartments or surfaces which articulate with the condyles of the femur. The medial condyle is more prominent anteriorly and broader both in the anterior-posterior and transverse diameters than the lateral condyle. Accordingly, the lateral articular surface of the tibia is shorter, more shallow and narrower than the medial surface of the tibia. The medial surface is broader, more circular, and concave from side to side. The anterior surfaces of the tuberosities are continuous with one another, forming a single large surface which is somewhat flattened. Posteriorly the tuberosities are separated from each other by a shallow depression for attachment of ligaments. The medial tuberosity presents posteriorly a deep transverse groove for the insertion of a tendon.
The patella is a sesamoid or lens shaped bone which slides in a groove between the condyles of the femur. Its function is to increase the efficiency of the quadriceps muscle by shifting the line of action of the muscle's pull forward. As the knee articulates, the muscles and tendons force the patella toward the condyles of the femur. Consequently, there is considerable relative motion between the patella and the other bones comprising the knee joint.
Because of aging or disease, the articulating surfaces of the knee may degrade. To treat certain pathologies, it has become common to surgically remove the condyles and replace these structures with prosthetic implants. By the same processes, the articulating surfaces of the patella may also degrade. In connection with the implantation of a prosthetic knee. therefore, the articulating surface of the patella may also be replaced. Because of the tendons connected to the patella, it is generally advisable to replace only the articulating surface. An ultra high molecular weight polyethylene articulating surface, with or without a metal baseplate, will be implanted on the posterior side of the patella, adjacent the femoral condyles.
To implant such a prosthesis, the posterior surface of the patella is resected to produce a flat surface upon which the prosthesis can be mounted. In the past, the surgeon often had to rely on skill of hand and eye in manipulating a sagittal saw in order to make an appropriate cut.
Prior art devices for aiding the surgeon in performing patella resections are well known to those skilled in the art.
For example, Petersen, in U.S. Pat. No. 4,633,862, issued Jan. 6, 1987, incorporated herein by reference, teaches a method and instruments for the installation of a patella button prosthesis which involves performing a patella resection.
In particular, Petersen describes a saw guide which comprises a pliers-like instrument having a pair of mutually pivotable jaw members. The jaw members are designed so as to enable them to surround the outer periphery of the patella, with each jaw member having a respective handle, integrally formed therewith, which handles may be pivoted so as to pivot the jaw members to and from engagement with the patella periphery. At the ends of the handles, a locking device is provided therebetween which enables the locking of the jaw members about the patella periphery.
Furthermore, Petersen's saw guide is so designed that the posterior sides of the jaw members are co-planer and these posterior sides of the jaw members define the plane of resection of the patella; and that attached to the saw guide and pivotable on a common axis with the axis of pivoting the jaw members are a series of wing gauges, a plurality of which are located on the posterior side of the saw guide; with a single further guide being located on the anterior side of the saw guide.
The anterior wing gauge is for the purpose of aiding the surgeon in determining whether the patella has been grasped at the correct location so that after resection adequate bone stock will remain. More particularly, the posterior wing gauges are provided so that the saw guide has adjustability; with one of these gauges being placed in a position to engage the most posterior portion of the patella. The anterior gauge is then pivoted into a position to determine if adequate bone stock will remain after resection. If the anterior gauge does not rotate freely, then sufficient bone stock remains.
As indicated hereinabove, saw guides of the type taught by Petersen utilize the co-planer posterior sides of the jaw members to define the plane of resection of the patella. After the patella has been properly positioned within the saw guide and the guide secured thereon, a saw may then be used remove the unwanted bone by manually placing and holding the saw flush against jaw member surfaces defining the aforementioned plane of resection through out the cutting process.
Dunn et al., in U.S. Pat. No. 4,759,350, hereby incorporated by reference for background purposes, describes in considerable detail (with reference to FIGS. 18, 19 and 20), a prior art process for preparing a patella for resection using a saw guide. The guide used is of the type described by Petersen at least in so far as requiring the saw to be manually held in place against the jaw member surfaces defining the aforementioned plane of resection while cutting the bone.
To improve the accuracy of cut over the type of guide devices described by Petersen and Dunn et al., improved saw guides are known which provide an integral saw capture slot within and through the aforementioned jaw members, for receiving and guiding a saw throughout the cutting process. Furthermore, guide devices are known which in addition to providing the aforementioned integral saw capture slot, also provide a rotating calibrated stylus for measuring the position of the patella with respect to the capture slot.
One such device is described by Whitlock et al. in U.S. Pat. No. 5,147,365, hereby incorporated by reference, issued Sep. 15, 1992, where the stylus is not only rotatable, but may also adjusted through displacement upwards and/or downwards before being locked into a desired position, to replace the plurality of wing gauges required by the Petersen type device.
In particular, Whitlock et al., describes a patella osteotomy guide for use by a surgeon in preparing a patella to receive a prosthetic articulating surface on the patella's posterior side.
According to the teachings of Whitlock et al., the guide captures a patella between jaws of a plier-like appliance. The jaws are curved for grasping a patient's patella, with a row of teeth facing inwardly from the jaws. The teeth are generally of pyramid shape, but a vertex of each tooth lies in a plane containing a bottom side of the respective jaw. This offset enables the teeth to grasp the patella in the middle. Each of the jaws has an integral saw capture slot extending along its length through which a sagittal saw may be inserted to precisely remove a selected portion of the patella. The tips of the jaws are extended so that the osteotomy guide may be used with larger patellas.
Furthermore, according to the teachings of Whitlock et al., the aforementioned rotating calibrated stylus accurately measures the position of the patella with respect to the integral saw capture slots. The stylus can be rotated so that a measurement can be made from the highest point of the patella, even if that point is asymmetrical with respect to the rest of the patella.
According to the preferred embodiment of Whitlock et al.'s invention, the rotating stylus also functions as a pivot or fulcrum about which the jaws and handles of the osteotomy guide rotate. Handles for the osteotomy guide are offset from the plane of the jaws to allow hand access without interference with the patellar tendon of the patient. A threaded rod and thumb nut are provided on the handles so that the guide may be clamped to the patella.
Still further, according to the teachings of Whitlock et al., the rotating stylus, as indicated hereinbefore, may be displaced up and down and then locked into a selected position using a draw bar and captured balls, effectively replacing the plurality of wing gauges described in the incorporated Petersen patent.
From a purely mechanical point of view, the rotating adjustable stylus integrated onto the type of guide taught by Whitlock et al., makes such a guide unduly complex, costly and subject to mechanical failure by virtue of the number of parts required to manufacture and use such a guide.
Furthermore, the calibrated stylus contemplated by Whitlock et al., requires the surgeon to visually determine a desired resection depth, and then lock the stylus in place at a prescribed, previously measured, location. The measurement, instrument placement and stylus setting procedures required by Whitlock et al. depend on the surgeon's vision and manual dexterity in operating the stylus, may be inaccurate and would not insure, for example, that a precise amount of bone (for example, precisely 6 mm, 7 mm, etc. of bone), could be removed during a given operation.
Still further, although the stylus arrangement taught by Whitlock et al., may be positioned "out of the way" during the resection process per se (by rotation), the stylus remains as a potential impediment to vision and guide manipulation since it is physically integrated on the guide.
Further yet, guides of the type taught by Whitlock et al. fail to easily accommodate the insertion of the saw into a capture slot. Such guides are potentially dangerous if a mishap should occur when trying to slide the saw into the capture slot, particularly since (at the time the saw is inserted) the patient is "open" and the operation is in progress.
For all of the reasons set forth hereinabove, it would be desirable to provide an easy to use resection guide that is mechanically simple, reliable and which enables a very accurate resection to be performed without having to rely on the surgeon having to measure and then set a desired resection depth using a calibrated stylus of the type described by Whitlock et al., prior to securing the resection guide.
In particular, it would be desirable if no such requirement for taking measurements and then accurately setting the stylus were required within a predetermined range of prespecified resection depths that are most often used when performing knee surgery, such as a range between 6 mm and 11 mm in 1 mm increments.
Furthermore, it would be desirable to provide a resection guide for which an accurate resection level may be easily set using a quick release stylus that easily attaches to (and may be quickly removed from) calibrated and marked steps on the resection guide, for visibility during resection.
Still further, it would be desirable to provide, in combination with the above desired features, a resection guide that is not only slotted, but also provided with a saw blade insertion guide to help avoid the aforementioned potential for injury if a mishap should occur when trying to slide the saw into the capture slot.